Cathode-ray tube apparatus for comparing two electrical signals



July 24, 1951 Filed May 10, 1945 D. C. CULVER CATHODE-RAY TUBE APPARATUS FOR COMPARING TWO ELECTRICAL SIGNALS 4 SINGLE CYCLE SWEEP GENERATOR STANDARD FREQUENCY GENERATOR PICKUP 1" l ELECTRONIC SWITCH AND AMPLIFIER PICKUP it 2 SINGLE CYCLE SWEEP GENERATOR 5 Sheets-Sheet 1 FIG. I

nmeso MIRROR CATHODE l RAY TUBE l i T 6 SHUTTER 4 :MIRRORS FIG. 2

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DONALD C. CULVER y 1951 D. c. CULVER CATHODE-RAY TUBE APPARATUS FOR COMPARING TWO ELECTRICAL SIGNALS 5 Sheets-Sheet 2 Filed May 10, 1945 ITE INVENTOR. DONALD C. CULVER $56 22 5:3 -25 232 55 J 5 5m 6. Q A

w L p To 3 mm :1 @N J i xokdmw Sh; :25 .EE -zutu -fix I h 8 Km 8 2 July 24, 1951 D. c. CULVER CATHODE-RAY TUBE APPARATUS FOR COMPARIN TWO ELECTRICAL SIGNALS 5 Sheets-Sheet 3 Filed May 10, 1945 July 24, 1951 D. c. CULVER CATHODE-RAY TUBE APPARATUS FOR COMPARING TWO ELECTRICAL SIGNALS 5 Sheets-Sheet 4 Filed May 10, 1945 FIG. 7

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m m m m FUNCTION SWITCH INVENTOR. DONALD c. CULVER ATTORNEY.

July 24, 1951 o. c. CULVER CATHODE-RAY TUBE APPARATUS FOR CMPARING TWO ELECTRICAL SIGNALS Filed llay 10, 1945 5 Sheets-Sheet 5 i E A mm. o:

INVENTOR. DONALD C. CULVER ATTORNEY.

Patented July 24, 1951 CATHODE-RAY TUBE APPARATUS FOR GOM- PARING TWO ELECTRICAL SIGNALS Donald C. Culver, South Ardmore a a or.

by mesne assignments, to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a

corporation of Delaware Application May 10, 1945, Serial No. 593,039

6 Claims. (Cl. 171-45) The present invention relates generally to vibration indicating and recording apparatus and has especial utility for obtaining data useful in analyzing vibration and flutter phenomena in aircraft during flight.

As the flying speeds of aircraft have increased, the need for instruments providing data useful in analyzing vibration and flutter of the aircraft structure during flight has become more urgent because of the occurrence of many fatal and apparently unexplainable accidents in the air. Airplanes in flight have been seen disintegrating, apparently exploding. Investigation, however, has revealed that they did not explode and has indicated further that disintegration occurred as a result of extremely violent vibration or shaking of the aircraft structure.

Such vibration and shaking, termed "flutter," appears at certain critical speeds and is so sudden that wings and tail surfaces are broken oil. before the pilot can change the speed. The violent flutter is believed to occur when the pulsating aerodynamic and other forces acting upon the aircraft synchronize with the natural resonance of the aircraft structure. It appears that the phase relations of the vibrations at various points on the structure, as well as the frequencies and amplitudes of the vibrations. play an important part in the generation of flutter.

It has been proposed, in the prior art, to analyze the vibration or flutter characteristics or tendencies of aircraft in flight by providing a number of vibration detectors or pick-up units at various displaced points on the structure and by providing measuring apparatus for simultaneously recording the wave shapes, frequencies and amplitudes of the vibrations at such points. The prior art measuring equipment, however, has been exceedingly bulky and cumbersome and heavy, weighing from 300 to 500 pounds. This has prevented its installation and use in many light types of aircraft. Moreover, little or no information as to the phase relations of the vibrations at the displaced points on the structure was obtained. In addition a great amount of time, usually as much as ten days, was required to obtain even such meagre information.

A general object of the present invention is to provide an instrument characterized by its portability, light weight, and ability in conjunction with suitable vibration pick-up units to provide in a matter of a few hours more information regarding vibration and flutter phenomena of aircraft in flight than has heretofore been obtainable.

2 Another object of the invention is to provide such an instrument which is capable of being mounted and operated in any position in an aircraft cockpit, and if desired, held in the lap of the pilot or other operator. A further objectis to provide such an instrument which will operate satisfactorily under the normal vibration and temperature conditions encountered in an aircraft cockpit.

It is an object of the invention also to provide an instrument of the above referred type which is capable of simultaneously making permanentrecords of the wave shapes, frequencies, amplitudes, and phase relations of the'vibrations or flutter at a pair of displaced points on the aircraft structure and is adapted to provide such records of a large number of such pairs of displaced points in rapidsuccession. A more speciflc object isto provide such an instrument in-- corporating suitable means for visual observation of the peak-to-peak amplitudes of the vibrations and adjustment of the instrument until thetwo traces to be recorded are of amplitude suited manipulation so as to provide a substantially linear record of the vibration.

Still another object of the invention is to provide a flight vibration recorder operable to provide records which are substantially faithful replicas of vibration frequencies from 5 to 300 cycles per second.

In one speciflcvembodiment of the invention,

two separate and similar channels for ampliflcation and recording are provided so that simultaneous records may be obtained for each of two externally connected vibration pick-up units.

Each amplifier channel is so chosen as to be suitable for operation with velocity-type vibration pick-up units having internal impedance from 5 to 500 ohms and for strain gauge elements with internal impedance from 500 to 30,000 ohms and providing a satisfactory output signal for input voltages varying from 0.5 mlllivolt to 2.0 volts.

Photographic means are provided for recordingthe output signals, the separate records being displaced on the fllm so as to avoid overlapping of the individual. traces and being of at'least 3 one half inch peak-to-peak amplitude for the above mentioned input voltages. A high impedance step-type attenuator is provided for each amplifier channel to suitably relate the output signal amplitudes to the amplifier voltage gain in a suitably large number of ratios.

It is a specific object of the invention to provide in such an instrument means for varying the number of complete cycles per inch appearing on the record and, if desired, for limiting to a suitable value the number of cycles per inch for any frequency in the range of measurement.

It is a specific object also to provide means for readily adjusting the relative positions of the separate traces on the record.

A still further specific object of the invention is to provide a novel electronic switching arrangement for alternately impressing during mutually exclusive intervals first and second electrical signals on the beam deflection plates of a cathode ray tube having a screen and including suitable means to separate the traces of each signal produced on said screen.

It is also an object of the invention to provide a novel relaxation oscillator arrangement for generating a sweep frequency signal of adjustable frequency which signal is recurrent in one condition of adjustment of the oscillator and in another condition of adjustment thereof comprises a single cycle or pulse.

A further object of the invention is to provide means for recording on each record a standard frequency timing wave, the frequency of which may be readily identified from its wave shape and which may be employed to provide a close approximation of the frequencies of the two vibrations being recorded.

Still another object of the invention is to provide a novel circuit arrangement which is both simple and eflicient for generating such a standard frequency timing wave and which incorporates suitable provisions for changing the frequency of said wave.

Another specific object of the invention is to provide simple and efficient means for making a large number of vibration records in rapid succession. To this end, simple and rapidly operable means are provided for advancing or changing the film between records.

It is another object to provide such flight vibration recording apparatus which includes conveniently placed and properly marked dials for selecting the proper time axis for the recorder. for providing voltage outputs of each amplifier channel suitably related to the amplifier voltage gain. and for obtaining the desired records.

The flight vibration recorder of the present invention is characterized in that data making possible a more complete analysis of the vibration and flutter characteristics of aircraft in flight may be obtained in a matter of a few hours. The entire instrument, moreover, inc uding the energizing batteries and recording apparatus, is of very light weight. In a preferred and satisfactory operating embodiment of the invention, the complete instrument including its energizing batteries weighs only 2'7 pounds and its dimension are 6" x 12%" x 16 thus permitting its use in even the smallest type airplanes. construction, described in detail thereinafter and providing suitable means for making visual observation of the vibration and flutter phenomena during the flight of the aircraft, is completely selfcontained and includes batteries, two electronic amplifying channels each containing a suitable This preferred integrator and an electronic switch, a cathode ray oscillograph, means for observing the traces as they appear on the oscillograph screen and a camera which photographs the record. The instrument is capable of simultaneously providing on a single cathode ray oscillograph screen and of recording on a single film traces corresponding to the vibration and flutter phenomena at two displaced points on the aircraft structure, thus facilitating comparison of the wave shapes and amplitudes of the two traces and making possible determination of the phase relation existing between the vibrations at the displaced points on the aircraft structure. The vibration and flutter phenomena at more than two points on the aircraft structure may be recorded by means of the use of a selector switch for connecting pairs of displaced points on the aircraft structure in succession to the flight vibration recorder. Provision is also made in the recorder for projecting a time reference on the screen of the cathode ray oscillograph which is included in the photographic records for facilitating determination of the vibration frequencies at the various pairs of points on the aircraft structure.

The variou features of novelty which characterize this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying drawing and descriptive matter in which is illustrated and described a preferred embodiment of the invention.

Of the drawings:

Fig. 1 is a schematic illustration of one form which the vibration recording and viewing ap paratus of my invention may assume;

Fig. 2 illustrates a modification of the arrangement of Fig. 1 wherein only a single cathode ray tube is utilized;

Fig. 3 illustrates a modification of the circuit arrangement of Fig. 2, constituting a preferred form of my invention for use in analyzing the vibration and flutter phenomena in aircraft;

Fig. 4 illustrates in detail the attenuators. amplifiers, integrators and electronic switches of the arrangement of Fig. 3;

Fig. 5 is a graph showing the manner in which the integrators of Figs. 3 and 4 operate to change the character of the signal under detection;

Fig. 6 is a schematic illustration of one form of multi-vibrator which may be employed in the arrangement of Fig. 3;

Fig. 'l is a graph illustrating representative wave shapes adapted to be produced by the marking signal generator of Fig. 3;

Fig. 8 is a graph illustrating the relation of the vibration traces and of the marking signal and is representative of the photographic patterns obtained with the preferred embodiment shown in Figs. 3-6;

Fig. 9 is an elevational view, with some parts broken away, of my preferred flight vibration recorder construction, showing the various control devices and the means for visually observing the oscillograph record and the means for making the photographic record;

Fig. 10 is a view taken along the lines A-A in Fig. 9:

Fig. 11 is a view taken along the line 3-3 in Fig. 10; and

Fig. 12 is a view t ken along the line 0-0 in Fig. 9,

For the purpose of illustration, the various apparatus embodiments disclosed herein have been described as applied to permit visual observation and to obtain photographic records of the vibration and flutter of aircraft durin flight. It will be understood, however, that the physical embodiments of my invention are not restricted to such use but are applicable generally wherever it is desired to inspect and make permanent records of the relative wave shapes, amplitudes, frequencies and phase relations of the vibrations at displaced points on any vibrating structure and also are adapted to provide inspection and recording of the same characteristics of two undulating voltages regardless of their manner of derivation.

Referring now to Fig. l, disclosing in schematic form one embodiment of my invention, it will be seen that the vibration recording instrument includes two cathode ray tubes of known type having electron stream forming means as well as vertical and horizontal deflecting plates and indicated by the reference characters I and 2, and a camera 3 comprising a lens 4, a movable shutter 5, and a film G, as well as a mirror arrangement 1 for reflectin the traces on each of the cathode ray tube screens on the lens 4. The mirror arrangement I includes a hinged mirror 8 positioned in front of the screen of the cathode ray tube I and a hinged mirror 9 positioned in front of the screen of the oathode ray tube 2. A relatively stationary member I positioned between the hinged mirrors 8 and 9 and havig two reflecting surfaces disposed at an angle with respect to each other is also provided. One reflecting surface of member III is associated with the hinged mirror 8 and the other is associated with the hinged mirror 9 for completing the optical paths from the screens of the cathode ray tubes I and 2, respectively, to the lens 4 when the hinged mirrorsare in the positions shown in dotted lines.

The vibration recorder also includes two electronic signal amplifying channels designated generally by the reference numerals II and I2, a standard frequency generator I3, a single cycle sweep generator I4, and a three-gang, three position switch designated by the character I5. If desired, a push-button or the like switch may be employed in place of the switch l5 for greater convenience.

Each signal channel II and I2 includes a pickup unit of suitable type and electronic amplifying means. Thus, the channel II includes a pick-up unit I6 and an electronic amplifier I I while the channel I2 includes a pick-up unit I I and an electronic amplifier I9. The pick-up units I6 and I 8 are mounted at displaced points on the structure of an airplane in flight and are operative to create undulating signal voltages of wave shape, amplitude, frequency and relative phase relation corresponding to the character of the vibration or flutter at the said points on the airplane structure.

In position b of the switch I5, the amplifiers I1 and I9 in the two pick-up channels are connected to the associated vertical deflecting plates of the cathode ray tubes I and 2, while the standard frequency generator I3, which generates saw tooth waves, is connected to the horizontal deflecting platss of both of the cathode ray tubes. Preferably, the hinged mirrors 8 and 9 and the camera shutter 5 are mechanically coupled to the switch I5 so that when the latter is in its position b, the camera shutter 5 is closed and the hinged mirrors 8 and 9 are in their full line positions, and'the traces on the cathode ray tubes I and 2 may be viewed directly. If desired, the said traces may be observed by means of mirror means (not shown) which may be provided near the lens I in the same manner as is illustrated in Fig. 9. When the cathode ray tube traces are viewed by such alternative mirror means, the hinged mirrors 8 and 9 are adjusted into and continuously maintained in their dotted line po sitlons.

This observing or viewing position of the switch I5, shutter 5, and mirrors 8 and 9 is provided for the purpose of enabling the observer to inspect the peak-to-peak amplitude of the traces in order to permit adjustment of the signal amplification until traces of the amplitude suitable for recording on the fllm 6 are obtained. To this end each of the amplifiers I1 and I9 desirably includes suitable means to adjust the signal ampliflcation. Such means for adjusting the signal amplification may comprise means known and available in the prior art for such purposes. By way of example, attenuating means as disclosed in Figs. 3 and 4 and described hereinafter may be employed. It is noted that a defined trace pattern will not be obtained in most cases since no provision is made for adjusting the standard frequency generator to a frequency commensurate with the signal frequencies. If desired, however, an adjustable standard frequency generator may be provided for permitting such adjustment of the horizontal sweep frequency on the cathode ray tubes.

After amplitude adjustment of the traces on the cathode ray tube screens has been effected, switch I5 is adjusted into its position 0, in which the amplifiers remain connected to the respective vertical deflecting plates of the cathode ray tubes I and 2, while the horizontal platcs are switched to the single cycle sweep generator I4. The generator I4 is actuated by the switching action and produces a single horizontal linear sweep at a predetermined speed. Preferably, the speed of the sweep is adjustable, in steps, so as to make the sweep speed commensurable with the signal frequencies. To this end the single cycle sweep generator may be of the type disclosed and described in connection with Fig. 3. It is noted that the provision of a single sweep eliminates the necessity of adjusting the rate of sweeping speed to match the signal frequencies.

When the switch I5 is brought into position 0, the shutter 5 of the camera is opened so that the trace may be recorded on the film. At the same time the optical path from the cathode ray tube screens and the lens l to the observer is closed so as to prevent extraneous light from falling on the fllm.

After having recorded the traces on the screens of both cathode ray tubes I and 2 in the manner just described, the switch I5 is moved into its position d in which the standard frequency generator is connected to the vertical deflecting plates of one or both of the cathode ray tubes. while the single cycle sweep generator I4 remains connected to the horizontal plates. The

switching action again releases the sweep generator and a trace produced by the standard fre-..

quency generator is also recorded on the film and serves as a marking indicative of time with which the recorded signals can be compared to determine their frequency, at least approximately. In the position 11 of the switch I5 theshutter 5 remains open and the hinged mirrors 8 and 9 are in their dotted line positions.

Upon completion of the foregoing operations.

7 the switch I! is returned to its position b, the exposed film is removed, and the instrument is ready for preparation for the next observing and recording operations.

In the measuring instrument disclosed in Fig. 1, it is contemplated that the pick-up units It and I0, the amplifiers l1 and I9, and the standard frequency generator I! and the single cycle generator I may all be of known type. One form which each of these units may take, however, is disclosed in Figs. 3-6 wherein I have illustrated in detail a preferred embodiment of the invention. The pick-up units it and II may be of the velocity type or may be of the strain gauge type, both of which types are now commercially available. It is noted that when the pick-up units It and II are of the velocity type the undulating signal voltages created thereby vary in accordance with a differential function of the vibration or flutter to which the pick-up unit is responsive, and hence, it is desirable to include in the amplifiers l1 and is suitable means to integrate the signal voltages to derive a voltage undulating in linear accordance with the vibration or fiutter under observation. One arrangement which may be employed for this purpose is shown in Fig. 4.

In order for the measuring equipment of Fig. l to be completely self-contained, thereby enhancing its usefulness as a portable instrument, it desirably is designed for D. C. operation and to this end suitable batteries are provided to supply the necessary amplifier, standard and single cycle sweep frequency generator and cathode ray tube currents and voltages.

Due to the relatively heavy filament current required by cathode ray tubes, which is supplied by batteries, the arrangement shown schematically in Fig. 2 is now considered preferable over that of Fig. 1 in that only a single cathode ray tube, indicated by the numeral 20, is required. In order to permit simultaneous recording of both vibration signals by means of the single cathode ray tube, an electronic switch is provided for combining the said signals. The electronic switch may be of known type and desirably may be incorporated in an electronic switch and electronic amplifier indicated by the numeral 2 I. A two-gang switch indicated at lBa is provided for accomplishing the desired observing and recording operations. The arrangement of Fig. 2 also includes a standard frequency generator I, a single cycle sweep generator ll, a camera I, and a hinged mirror 22 and an associated stationary mirror 23 for reflecting the traces on the screen of cathode ray tube 20 to the lens I.

It is believed that the operation of this embodiment of my invention will be evident from the description of the operation of the arrangement of Fig. 1, particularly in view of the description given hereinafter of the arrangement of Figs. 3-12. Suflice it to say at this point that the electronic switch and amplifier 2| operates to alternately impress at high speed on the vertical deflecting plates of the cathode ray tube 2| the vibration signal voltages created by each of the pick-up units It and II. Thus, simultaneous traces are produced on the screen of the oathode ray tube corresponding to each of the vibration signals. Preferably, suitable means are incorporated in the arrangement for separating the traces so that they do not overlap and are readily distinguishable. Means for accomplishing this result are disclosed and described in connection with Figs. 3 and 4 hereinafter.

In Figs. 3 through 12 I have illustrated, more or less diagrammatically, a preferred embodiment of my invention, comprising a two channel vibration indicator and recorder which is self-contained and is adapted to be carried on the lap of the pilot or observer. This preferred embodiment provides simultaneous recording of two individual vibrations and also of a marking signal of known frequency for determining the frequencies of the recorded vibrations. The instrument constituting my preferred embodiment is battery operated, completely self-contained, small in overall dimensions, and light in weight and is particularly useful in making tests of equipment where space is limited and weight is an important factor. For clearness of illustration, parts corresponding to those in Figs. 1 and 2 have been indicated by the same reference characters in Figs. 3-12.

The vibration recorder shown schematically in Fig. 3 includes two electronic signal amplifying channels indicated generally by the numerals 24 and 25, and each of which includes an attenuator, a first amplifier, an integrator, and a second amplifier. The channels 24 and 25 may be identical and are shown in detail in Fig. 4. Channel 24 includes an attenuator 26, a first amplifier 21, an integrator 28, and a second amplifier 29, while the channel 25 includes an attenuator 80, a first amplifier ll, an integrator I2 and a second amplifier l3. Vibration pick-up units It and I. are connected to the input terminals of the attenuators 26 and Ill, respectively. The vibration pick-up units may be of either the velocity type or of the linear strain gauge type. Attenuators 26 and 30 are provided to regulate the amplitude of the signal voltage impressed on the input circuit of the associated first amplifier from the vibration pick-up units.

A two-gang, two position switch indicated at 34 is provided for connecting the integrator 2! into the channel 24 or for disconnecting it from that channel. A similar two-gang, two position switch indicated at I! is provided for inserting or removing the integrator 32 from the channel 2!. In positions 0 of each of the switches 34 and ll, the integrators 28 and 32 are disconnected from their associated channels and the output circuit of each first amplifier 21 and II is connected to the input circuit of its associated second amplifier 29 and II. The switches 34 and 35, when adjusted to their positions b, connect the integrators 2t and I2 between the output circuit of the first amplifier and the input circuit of the second amplifier of the associated channel. Preferably, the switches 84 and II are ganged together so that the insertion and removal of the integrators 28 and 32 from their associated channels may be accomplished by means of the manipulation of a single control device or knob.

The arrangement of Fig. 3 also includes a pair of electronic switches designated by the characters 38 and 31, a multivibrator a, a third amplifier indicated generally by the numeral ll, a cathode ray tube 20, a combined standard frequency and single cycle sweep generator indicated generally by the character ll, and a marking signal or time reference generator designated generally at ll. A camera 3, comprising a hinged mirror 22, a lens 4, a shutter I and a film t is provided for recording the traces on the screen of the cathode ray tube 2!. Suitable means as described in connection with Figs. 9, l0 and 11 are provided for permitting visual observation of the cathode ray tube screen.

In the normal operation of the instrument, signal voltages created by the vibration pick-up units are impressed on the input terminals of each'of the attenuators 26 and 30 which, depending upon their adjustment, impress more or less of the bivration signal voltages on the input terminals of their respectively associated first amplifiers 21 and 3|. From the first amplifiers 21 and 3|, the amplified vibration signal voltages are impressed on the input terminals of the second amplifiers 29 and 33 either directly or through the associated integrator 28 or 32, depending upon whether the switches 34 and 35 are in their position or in their position b.

Each of the amplified vibration signal voltages is further amplified by the second amplifiers in the channels 24 and 25. Passing from the second amplifiers the amplified vibration signal voltages in each channel are impressed on the input circuit of the respectively associated electronic switch 36 or 31. The electronic switches 36 and 31 operate to alternatively impress at the frequency of 25,000 cycles per second first one amplified vibration signal voltage and then the other on the input circuit of the third amplifier 39. This high speed and alternate switching action is accomplished by means of the operation of the multivibrator 38 which keys the electronic switches 36 and 31, the keying being such that one switch is conductive while the other is nonconductive. The input circuits of the electronic switches 36 and 31 are biased to different extents and different screen grid voltages are employed, as is explained in detail hereinafter, so thatthe extent to which the electronic switch 36 is adapted to become conductive to pass vibration signal voltages of normal amplitude is different from that to which the electronic switch 31 is adapted to become conductive to pass vibration signal voltages of corresponding amplitude.

From the third amplifier 39 which operates to further amplify each of the vibration signal voltages, the amplified vibration signal voltages are impressed on the vertical deflecting plates of the cathode ray tube 20. The output terminals of the sweep generator 40 are connected to the horizontal deflection plates of the cathode ray tube. In one of its operating conditions the sweep generator 40 impresses a recurrent sweep voltage on the horizontal deflectin plates of cathode ray tube 20 for permitting observation of the signal voltage traces on the screen of the cathode ray tube, while in its other operation condition it impresses a single sweep voltage on the horizontal deflecting plates for photographic recording. A two-gang, two position switch indicated generally at 42 is provided for adjusting the sweep generator into one or the other of its operatin conditions. A push-button 43 is provided, as shown, so that when the sweep generator 40 is adjusted to its operating condition in which it produces only a single voltage, the occurrence and impression on the horizontal deflecting plates of the cathode ray tube 20 of that single voltage are delayed until the pushbutton 43 is closed. The switch 42 constitutes part of a switching arrangement referred to hereinafter as a function switch.

By means of a two position switch indicated at 44, the output terminals of the marking signal generator 41 may be connected to the vertical deflecting plates of the cathode ray tube 20 and the output circuit of the third amplifier 39 film as that on which the vibration signals are" recorded. Suitable bias means are provided when the markin signal generator is connected to the vertical deflecting plates of the cathode ray tube 20 so that the trace produced thereby is vertically displaced from the vibration signal voltage traces. Since the input circuits of the electronic switches 36 and 31 are biased to different extents, the vibration signal voltage trace representing the vibration signal voltage transmitted through channel 24 will be vertically displaced from the other vibration signal voltage trace.

In Fig. 4 I have illustrated in detail one practical operating arrangement of the channels 24 and 25. Since the channels 24 and 25 are identical, only one channel has been shown in detail in Fig. 4. It is noted that both channels not only are identical but both may be, and preferably are, supplied with energizing voltages from the same batteries. Such double utilization of the energizin batteries is desirable inasmuch as it reduces both the overall dimensions and weight of the instrument. Fig. 4 also shows one practical working arrangement of electronic switch 36 or 31 which may be employed and its manner of connection to the output terminals of the respectively associated channel 24 or 25. The electronic switches 36 and 31 may be and preferably are identical as to the components contained and their manner of interconnection, but as previously noted, different biasing voltages are impressed on their input circuits and different voltages are impressed on their screen grid circuits for the purpose of eifectuating vertical displacement on the screen of cathode ray tube 20 of the two vibration signal traces. The specific differences between the two electronic switches 36 and 31 will become apparent as the description proceeds. In order to maintain at a minimum the number of batteries required in the instrument, the same batteries preferably are employed for energizing both of the electronic switches.

For convenience of illustration it will be assumed that the channel and electronic switch shown in Fig. 4 constitutes the channel 24 and the electronic switch 36. It will be understood that the explanation of the construction and manner of operation of this channel and electronic switch will apply also to the other channel 25 and electronic switch 31.

The attenuator 26, as shown in Fig. 4, is a high impedance step type attenuator and is provided for the purpose of reducing the amplitude of the vibration input signals before impressing them on the input circuit of the first amplifier 21. Such reduction is desired in order to suitably relate the amplitude of the vibration input signals to the overall amplification of the channel 24 and of the third amplifier 39 so that traces of the proper amplitude are produced on the screen of the cathode ray tube 20. Thus, it is possible by a simple manipulation of the control dials of the attenuators 26 and 30 to so adjust the amplitudes of the vibration signal traces that the amplitudes of both traces are approximately the same with no overlapping-of the traces. Accordingly, the vibration signal traces are readily distinguishable from each other when the attenuators '26 and 30 are properly adjusted.

As shown, the attenuator 26 is made up of a number of series connected resistances R1 through R13, a corresponding number of stationarycontact points b through 0, and a contact arm 1) pivoted at one end and adapted to engage one of the contacts 1) through depending upon the position to which it is adjusted. Essentially, the attenuator 25 is a voltage divider resistance, the full vibration signal voltage generated by the pick-up unit l5 being impressed across all of the resistances R1 through R1: in series, and a variable part of that voltage being tapped of! by the switch arm p depending upon which contact b through 0 it happens to engage.

By way of illustration, it is noted that the val ues of the resistances R1 through R1: in a working arrangement of the preferred embodiment of my invention are as follows:

. When the values of resistances R1 through Ru are so chosen, the attenuator 25 provides voltage outputs related to the full amplifier voltage gain in the following ratios: 1.0, 0.5, 0.25, 0.1, 0.05, 0.025, 0.01. 0.005, 0.0025, 0.001, 0.0005, 0.00025, and 0.0001.

The first amplifier 21 comprises a resistance coupled stage and incorporates suitable means known in the art to provide low frequency compensation for the purpose of providing a signal in its output circuit having a linear frequency response for frequencies varying at least over a range of 5 to 300 cycles per second. The low frequency compensation is obtained by means of a resistance 45 and a parallel connected condenser 45 in the plate load of the vacuum tube 41 included in the amplifier 21.

Tube 41 is a pentode type and desirably is of the commercially available type 1L4 including plate, suppressor grid, screen grid, control grid and filament type cathode elements. This tube of the miniature type, has been found to give satisfactory results as a high gain, wide band amplifier tube as it is employed in amplifier 21. Its small size and low filament drain enhance its usefulness in the preferred embodiment of my vibration recorder. Energizing current is supplied to the filament type cathode from a low voltage "A" battery designated by the character Al and which also is connected to and supplies energizing current to the filament type. cathodes of tubes 40 and 40, respectively included in the second amplifier 20 and the electronic switch It.

. Preferably, the battery Al also is connected to 12 designated by the character CI. The negative terminal of battery Cl, which may desirably provide six volts between its positive and negative terminals, is connected to the stationary contact 0 on the attenuator 25, while the movable contact arm :1 is directly connected to the control grid of tube 41. Accordingly, a unidirectional potential from battery Cl and an undulating vibration signal from the pick-up unit 15 are impressed in series between the cathode and control grid of tube 41, the potential from battery Ci operating to render the control grid suitably negative in potential with respect to the poten-- tial of the cathode for the proper operation of tube 41.

Plate and screen grid voltages are suppliedthe tube 41 from a B battery designated by the character BI and which is utilized also to supply plate and screen grid voltages to the tube 40 of the amplifier 29. Preferably, the battery Bl also supplies plate and screen grid voltages to the tubes included in the amplifiers 2i and 33 of the channel 25. Battery BI is a high voltage battery including both and volt taps and also additional voltage taps not employed for energizing the channels 24 and 25 but otherwise employed. The negative terminal thereof is connected to the negative terminal of battery Al and thereby to the corresponding terminals of the filament cathodes of each of the tubes included in the amplifiers 21, 29, 3| and 33 while the 90 volt tab is directly connected to each of the screen grids and the 180 volt tap is connected to supply energizing voltage to each of the plate circuits. 'The plate circuit of tube 41 may be traced from the positive 180 volt tap on battery BI through the parallel connected resistance 45 and condenser 45, a resistance 50, the plate of tube 41, and the cathode thereof to the negative terminal of battery BI.

The plate circuit of the tube 41 is resistancecapacity coupled to the input circuit oi the second amplifier 29, either directly or through the integrator 28 depending upon the position to which the switch 84 is adjusted. Specifically, the plate of tube 41 is connected by a condenser 5| to the left switch arm of switch 54 as seen in the drawing. A resistance 52 having its upperterminal connected to the condenser 51 when the switch 34 is in its position 0, has its other terminal connected through the battery C1 to the grounded terminal of the filament cathodes of tubes 41 and 48. By means of this connection the undulating voltage component appearing in .1

the plate circuit of tube 41 and constituting the amplified vibration signal is impressed on the resistance 52 which, in turn, is connected to the input circuit of the second amplifier 29. When the switch 34 is in its position b, the amplified vibration signal is impressed on the resistance 52 through the integrator 20.

As shown, the integrator 28 is comprised of a resistance 53 and a condenser 54 adapted to be connected in seriesin the order named between the condenser 5| and ground G when the switch 24 is in its position b. When switch 34 is in its latter position, the undulating voltage component appearing across the condenser 54 is impressed on resistance 52 and thereby on the input circuit of the secondamplifier 29. Accordingly, with the integrator 28 operatively connected between the first and second amplifiers, the vibration signal impressed on the input circuit of the second amplifier varies in accordance with the v '13 charge on the condenser 54, thus having the effect of integration, as those skilled in the art will understand and which it is believed will become evident from a study of the graph shown in Fig. and the following explanation.

In Fig. 5 the saw tooth curve VI represents the wave shape, frequency and amplitude of the vibration to which pick-up unit 18 is subjected. When the pick-up unit I8 is of the velocity type, it creates a vibration signal voltage having a square wave characteristic as shown by curve V2 directly below curve VI. Curve V2 represents the first derivative of the curve VI. Curve V3, directly below both of the other curves, represents the wave shape of the voltage appearing across condenser 54 of the integrator 28 and impressed on the input circuit of amplifier 29. It will be noted that curve V3 is substantially a replica of the curve VI This translation of the vibration signal appearing in the plate circuit of tube 41 having a wave shape as shown by curve V2 into a vibration signal having a wave shape as shown by curve V3 is accomplished by proper utilization of the char ing characteristic of a condenser. For example, on the positive half cycle of the square wave vibration voltage signal impressed on resistance 53 and condenser 54 of the integrator 28, the charge on the condenser 54 will gradually increase until the half cycle is over. On the next half cycle the polarity of the square wave vibration voltage reverses, causing the charge on condenser 54 to gradually decrease. Consequently, a sawtooth voltage wave of the shape shown in curve V3 is produced across the condenser 54. This sawtooth wave corresponds exactly to the original vibration being indicated and recorded and varies linearly with respect thereto.

While, for purposes of illustration, sawtooth and square waves have been referred to and shown, it will be evident that such integration will be efiectuated by the integrator 28 regardless of the characteristic wave shapes of the original vibration and the vibration signal voltage produced by the pick-up unit l8. It will be understood thatwhen the vibration pick-up unit I8 is of a type which develops a vibration signal voltage varying in linear accordance with the vibration under detection, it is not necessary to employ the integrator 28, and therefore, the latter is switched out of the network by adjustment of the switch 34 to its position 0.

The second amplifier 29 comprises a resistance coupled stage which is substantially identical to the amplifier 21 and also includes low frequency compensation means comprising a parallel connected resistance 55 and condenser 58 connected in the plate load of tube 48 for assuring that linear frequency response of the signals in the output circuit of tube 48 is obtained at least over a range of frequencies varying from 5 to 300 cycles per second.

Tube 48 also is a pentode, and desirably of the commercially available type 1L4, and includes the same elements as tube 41. As previously noted, filament energizing current is supplied tube 48 from battery AI and screen and plate voltages are supplied tube 48 from battery Bl. The input circuit of tube 48 may be traced from the control grid to the upper terminal of resistance 52, through the latter to the negative terminal of battery CI, and from the positive and grounded terminal of the latter to the filament type cathode. The plate circuit may be traced from the positive 180 volt tap on battery BI to the parallel connected resistance 55 and condenser 58, a resistance 51, the plate of tube 48 and the cathode thereof to the negative terminal of the battery.

The plate circuit of tube 48 is resistance-capacity coupled by means of a condenser 58 and a resistance 89 to the input circuit of the tube 49 included in the electronic switch 38. Tube 49, which may be of the type known as pentagrid converters and desirably of the miniature, commercially available type 1R5, includes a plate, a suppressor grid element, a pair of screen grid elements, a pair of control grid elements, and a filament type cathode to the latter of which energizing current is supplied by the battery Al and the positive terminal of which is grounded at G. The control grid of the tube 49 ordinarily regarded as the second control grid is connected through condenser 58 to the plate of tube 48 and is also connected through resistance 59 to the 3 volt negative tap on a C battery designated by the character C2. Battery C2 is also provided with 1% volt, 6 volt, 10% volt and 13% volt taps, but in order to avoid complication of Fig. 4, only the 1% volt and 3 volt taps are shown therein. The positive terminal of battery C2 is connected to the filament cathode of tube 49. Thus, battery C2 is utilized to provide a proper biasing potential for the second control grid of tube 49.

Battery C2 is employed also to provide suitable biasing potentials to the input circuit of amplifier 39 and sweep generator 48 as well as to the input circuit of the tube included in the electronic switch 31 and corresponding to the tube 49. It is noted that the second control grid of the tube in switch 31 is connected through a resistance corresponding to the resistance 59 to the 1% volt negative tap on the battery C2. Biasing voltage is supplied to the first control grids of each of the tubes in the electronic switches 36 and 31 from the 3 volt negative tap on battery C2 so that the first control grid of each tube is biased to the same extent. As shown in Fig. 4, the first control grid of tube 49 is connected through a resistance 60 to the negative 3 volt tap of battery C2. The first control grid also is connected to a first output circuit of the multivibrator 38 by means of a conductor 6 I. The first control grid of the tube in the electronic switch 31 is connected by a conductor 62, as seen in Fig. 3, to a second output circuit of the multi-vibrator Plate and screen grid vol-cages are supplied to the tube 49 and also to the tube in electronic switch 31 from a B battery designated by the character B2 and provided with 45 volt, 67% volt, volt, and volt taps. In Fig. 4 the 180 volt tap of battery B2 has been omitted to simplify the drawing. The plate circuit of the tube 49 may be traced from the positive 90 volt tap on ba.tery B2 through a parallel connected resistance 63 and a condenser 84, an inductance element or peaking coil 85, a resistance 86 to the plate of tube 49 and the filament cathode to the negailve terminal on battery B2. In the electronic switch 38 the screen grids of tube 49 are connected to the positive 45 volt tap on batter B2 while in the switch 31 the screen grids of the corresponding tube are connected to the positive 67% volt tap.

This difference in the potentials on the second control grids and on the screen grids of the tubes in the electronic switches 38 and 31 is provided so that the tube in switch 31 will have a larger plate current than the tube 49 in switch 38. By virtue of the plate current difference, the two output vibration signal voltages from the electronic switches 35 and 31 are impressed at different levels through the same channel on the vertical deflecting plates of cathode ray tube 20. As a consequence, the traces produced on the oscillograph screen and corresponding to the two vibration signal voltages are vertically displaced from each other, do not overlap, and are readily distinguishable.

In the preferred embodiment of my invention, the tubes in the electronic switches I and TI are keyed 180 out of phase with each other and at the high frequency of 25,000 cycles per second by voltages of square wave characteristic derived from the multi-vibrator II and impressed on the first control grid of each tube as aforementioned. Thus, the square wave voltage impressed on one first control grid operates to render its associated tube non-conductive during one half cycle while the square wave voltage impressed on the other first control grid operates to render the associated tube non-conductive during the other half cycle. As a consequence, one tube conducts during one half cycle and the other tube conducts during the next half cycle of the high frequency voltage output of multi-vibrator 38 whereby the vibration signal voltages in the channels 24 and 25 are impressed during alternate half cycles of said high frequency on'the input circuit of the third amplifier 39 and are reproduced during said alternate half cycles in the output circuit of amplifier 39, and consequently, are alternately impressed at said high frequency on the vertical deflecting plates of cathode ray tube 2|. While each trace on the screen of the cathode ray tube appears continuous, it is, therefore, actually composed oi a series of dashes each representing one half of the high frequenc keying cycle. The keying frequency is so high, however, that the dashes appear to merge and present apparently continuous traces.

The parallel connected resistance It and condenser 64 in the plate circuit of tube 40 are employed to provide low frequency compensation for assuring that the vibration signal will have a linear frequency response at least over the range of 5 to 300 cycles per second. Since the electronic switches 36 and II are keyed at the high frequency of 25,000 cycles per second, it is desirable to also provide high frequency compensating means in the plate circuits of the tubes of the electronic switches to assure the attainment of such linear frequency response. Such high frequency compensation is obtained by means of the peaking coil 65, the operation of which in accomplishing this end is known in the art and need not be described herein.

Merely by way of illustration, it is noted that each of the channels 24 and 25 and the electronic switches 36 and 31 in a practical operative construction utilizing the type tubes and battery voltages already mentioned is comprised of components having the following electrical characteristics:

- Resistance 45 ohms-- 50,000 Resistance 50 do-- 50,000 Resistance 52 megohm- 1 Resistance 53 ..do 0.25 Resistance 55 ohms 50,000 Resistance 51 do 50,000 Resistance 58 .megohm. 1 Resistance 50 --do 0.25 Resistance 03 ..ohms-- 20,000 Resistance 66 -do-..-- 15,000

16 Condenser 48 microfarads 4 Condenser 5| -do 0.1 Condenser 54 do. 0.1 Condenser 56 -do 4 Condenser 50 do 0.1 Condenser 04 do 16 Inductance element 65 millihenries 2.5

While the multi-vibrator 38 is essentially a relaxation oscillator and may be of known type, I prefer to employ a multi-vibrator of the construction shown in detail in Fig. 6 because that construction, at the relatively high frequency of operation of 25,000 cycles per second, provides oscillating voltages having a better square wave characteristic than it is possible to generate by the multi-vibrators of conventional type.

The multi-vibrator 30 shown in Fig. 6 comprises a two-stage resistance-capacitance coupled non-linear amplifier in which the output circuit of each stage is connected back to the input circuit of the other stage. The stages have been indicated by the reference numerals 61 and I, respectively. Stage 6'! includes a pentode tube 60 and stage 60 includes a pentode tube 10.

Each of the pentode tubes 69 and 10 may be of the commercially available miniature type 184 including plate, suppressor grid, screen grid, control grid, and filament type cathode elements. Energizing current is supplied to the filament type cathodes of the tubes 69 and ill from an "A battery designated by the character A2 and which provides 1% volts.

Plate and screen grid voltages are provided the tubes 09 and 10 from the battery 132, each of the screen elements being directly connected to the 67% volt taps, while the plate of tube 60 is connected through a resistance II to the 90 volt tap and the plate of tube 10 is connected through a resistance II to the 90 volt tap. The negative terminal of battery BI is connected through a biasing resistance [3 to the cathode of each tube.

As shown, a pair of series connected resistances I4 and I5 is connected between the negative terminal of battery B2 and the 90 volt tap and the point of engagement of these resistancesis connected to the junction point of one end of each of two resistances 16 and 11. The other end of resistance It is connected to the control grid of tube 60 and also through a condenser II to the anode of tube 10 while the other end of resistance I1 is connected to the control grid of tube 10 and also through a condenser I! to the anode of tube 00.

One output terminal of the multi-vibrator is connected through a condenser 8| to the anode of tube 69 and the other output terminal I! is connected through a condenser 83 to the anode of tube I0. The output terminal 80 is connected directly to the control grid of the tube 49 in the electronic switch 36 while the output terminal I! is connected directly to the control grid of the corresponding tube in the electronic switch 31.

.In the operation of the multi-vibrator 08, the

render one and then the other of said tubes non- 18 conductive at said high frequency.

Rcsistances 14 and I! connected across battery B2, provided for the purpose of permitting the use or a biasing resistance I8 of sumciently high value to produce the desired square wave shape at the output terminals 80 and 82 without resultant biasing of both tubes 88 and I to cut oil at the same time. This end is accomplished by impressing the positive voltage obtained across resistance I8 on the control grids oi tubes 88 and I0. In this manner it is possible to employ a biasing resistance of high value and at the same time operate the tubes voltages.

While there are commercially available several miniature tubes which may be employed in the multi-vibrator, I prefer to employ the 184 because of its high output and excellent stability. By way of illustration, when type 184. tubes are employed in the multi-vibrator 88 and the voltages referred to are impressed on the plate and screen grids, the various circuit components may desirably have the following characteristics:

Resistor II ohms 10,000 Resistor l2 do 10,000 Resistor I8 do 40,000 Resistor H megohm 0.1 Resistor I5 do 0.1 Resistor 78 d 0.1 Resistor II do 0.2 Condenser I8 micro-microfarads 100 Condenser I8 do 100 Condenser 8| microtarad 0.005 Condenser 88 do 0.

The markin signal generator I shown in detail in Fig. 3 is essentially a relaxation oscillator and is characterized in that it is operative in diflerent conditions of adjustment to generate oscillating voltages of diiferent frequency and also of correspondingly different wave shape. Accordingly, the frequency of the oscillating voltage produced by the marking signal generator and recorded by means of the cathode ray tube 20 and the associated camera 3 may be readily identified from the wave shape of the marking signal voltage, as may be seen by reference to Fig. '7.

.As shown, the marking signal generator 8i includes a tube 84 containing two similar triodes designated by the numerals 85 and 88 within the same envelope. Tube 88 may desirably be of the commercially available type 1G6. It is noted that the use of pentode tubes in place of each of the triodes 85 and 88 would make possible greater voltage output from the generator H, but this is not necessary or even desirable. In addition, the use of the one tube 84 adds to the compactness of the vibration indicator and recorder.

Triodes 85 and 88 each include plate, control grid and filament type cathode elements. Energizin current is supplied to the filament type cathodes from an A battery indicated by the character A8 and which is operative to provide 1% volts. the triodes 85 and 88 from the battery BI. the plate circuit of triode the positive 90 volt tap on battery BI through a resistance 81 to the plate of triode 85, the cathode thereof, and a selected one of three resistances 88, 88 or 80, dependin upon the position of a three position switch indicated at 8I, to the grounded and negative terminal of battery BI. Similarly, the plate circuit of triode 88 Thus, 85 may be traced from Plate voltage is supplied to each of as shown, comprise a voltage divider and are 88, and n at their normal bias I00 is provided for the may be traced from the positive 90 volt tap on battery BI through a resistance 82 to the plate of triode 88 and from the cathode to the negative terminal of battery BI through the selected one of resistances 88, 88, or 80. As shown, a condenser 88 is connected from the plate of triode 88 to ground.

The output circuit of triode 85 is coupled by means of a condenser 88 and a resistance 85 to the input circuit of triode 88. Specifically, the plate of triode 85 is connected by condenser 88 to the control grid of triode 88 and the said co trol grid is connected by resistance 85 to ground. The control grid of triode 85 is connected by a similar resistance 88 to ground. A switch indicated at 81 and comprising a part or the aforementioned i'unction switch is provided for short circuiting the resistance 85 for the purpose of stopping the oscillations of the marking signal generator. It is desirable to prevent the marking signal generator from oscillating during the ference with and distortion of those traces by the oscillations of the marking signal generator.

The output circuit of triode 88 is arranged to be coupled by means of a condenser 88, a resistance 88, a potentiometer resistance I 00 including a contact IOI adjustable therealong, and the switch 44, when the latter is in its position 0, to the vertical deflecting plates of the cathode ray tube 20. Potentiometer resistance purpose of adjusting the vertical position of the marking signal trace on the screen of cathode ray tube 20. To this end, one terminal of resistance I00 is connected to the positive 540 volt and grounded terminal battery indicated by the character B3, and the other terminal is connected to the positive 472 volt terminal on battery B3. Thus, a potential of 67 volts is impressed across resistance I00. A variable part of this voltage drop is adapted to be impressed on the cathode ray tube vertical deflecting plates depending upon the position along the length of resistance I 00 to which the contact IN is adjusted.

For purposes of illustration it is noted that the various circuit components 01' the marking signal generator may have the followin characteristics:

The marking signal generator 8|, as previously noted herein, is essentially a relaxation oscillator. Its manner of operation is generally like that of the so-called Potter circuit described in detail in a paper appearing on pages 713 to 719 of volume 26, Number 6 of the I. R. E. Proceedings dated June, 1938, and therefore, requires no detailed explanation herein. The character of the operation of the marking signal generator I is different in one important respect from the known Potter circuit, however, in that the frequency of oscillation is varied by changing the amount of cathode bias, as by connection of a selected one of resistances 80, as or 00, into the cathode circuit, instead of by variation in the value of one or more of the circuit components 01, 02, and 04 as contemplated in the above referred to paper. When the frequency of oscillation is varied by changing the cathode bias, the characteristic wave shapes of the oscillations at each different frequency are sufficiently different so that the frequency of the oscillations may be readily determined from their wave shape whereas there is little or no difference in the wave shapes of the oscillations of different frequency when the frequency variations are accomplished in the prior art manner, exemplified by the above paper.

In Fig. 7 I have illustrated representative wave shapes of the oscillations produced by the marking signal generator 4| when the switch 9| is adjusted into each of its positions b, c, and 11. Switch 0| is adapted to be adjusted into each of said positions for causing the generator to produce oscillations having frequencies of 24, 40, and 100 cycles per second, respectively, which oscillating frequencies and their characteristic wave shapes are shown by the curves MI, M2, and M0, respectively. It is apparent from even casual observation of these curves that they are readily distinguishable.

The sweep generator 40, disclosed in detail in Fig. 3, serves to provide a recurrent sweep for visual observation of the vibration signal and marking signal traces on the screen of the cathode ray tube 20, and also provides a single sweep for photographing. Referring to Fig. 3 it will be noted that the sweep circuit 40 includes in addition to the two-gang switch 42 and the push button 40, a condenser I02, a cold cathode discharge tube I02, a pentode tube I04, resistances I05, I00. I01, and I00, a condenser I09, a sweep frequency switch indicated at I I0, and a potentiometer resistance II2 having an associated contact H0.

The cold cathode discharge tube I03 may desirably be of the commercially available type 1C21 and includes plate, control grid and cathode elements. This tube does not utilize a hot cathode. and hence, requires no batteries for supplying filament energizing currents. Resist ances I00 and I06 are connected in series between the plate and cathode elements and their point of engagement is connected to the control grid. In position b of the two-gang switch 41 one terminal of condenser I02 is connected to the plate of tube I03 and the other terminal is connected to the cathode. Thus, with the twogang switch 42 in its position b the plate to cathode resistance of tube I03 and also the series connected resistances I00 and I06 are connected in shunt to the condenser I02.

Pentode tube I04 desirably is of the commercially available type 154 and includes plate, suppressor grid, screen grid, control grid and Illament type cathode elements. Energizing current is supplied the filament type cathode from the battery AI which also supplies energizing current to the filament type cathodes of the various amplifier stages and also of the electronic switches.

Switch H0 is a three position switch and is ganged together with the switch 9| employed in connection with the marking signal generator H for changing the frequency of operation of the latter. The switch H0 is provided for a similar purpose, namely to vary the sweep frequency of the sweep generator 40. In order to attain this end the switch III is adapted to selectively connect the control grid of tube I04 through resistance I00 to different negative voltage taps provided on the battery C2 to thereby change the bias voltage on the control grid. Specifically, in position b of switch III the control grid is connected to the negative 13% volt tap on the "6 battery C2 while in positions c and d the control grid is connected respectively to the negative 10% volt and 6 volt taps. The manner in which the sweep frequency of the generator 40 is changed by such variation of the bias voltage on the control grid of tube I04 will become apparent as the description proceeds.

Screen grid voltage is supplied tube I04 from the positive 45 volt tap on the B battery B2, the negative terminal of which is connected to ground (3 and thereby to the cathode of tube I04. Plate voltage is supplied the tubes I00 and I04 in series when switch 42 is in its position b from the positive volt tap on the battery 132 through a circuit which may be traced from the said 180 volt tap to one terminal of the parallel network comprised of condenser I02, tube I03, and the resistances I05 and I00, from the other terminal of the parallel network through the switch 42 to the plate of tube I04, and from the cathode thereof to the grounded and negative terminal of battery B2.

In the operation of the sweep generator 40. with the two-gang switch 42 in its b position, charging current flows into condenser I02 through the circuit including the plate to cathode resistance of the pentode tube I04 until the condenser potential reaches the ionization potential of the cold cathode discharge tube I00. The latter then breaks down and discharges the condenser I02 to the extinction potential of the tube I00 which then ceases to conduct and accordingly permits a charge to again build up on the condenser I02. In this manner the charging and discharging cycle of the condenser is made regularly recurrent, the time for each cycle being dependent upon the magnitude of the plate to cathode resistance of tube I04, which, in turn, is determined by the negative bias voltage impressed on the control grid of the latter.

Pentode tube I04 is employed in the circuit conducting the charging current flow to condenser I02 instead of ordinary resistance in order to make the charging rate of condenser I02 linear with respect to time. As those skilled in the art understand, the changing resistance of a pentode tube, as its plate potential changes, provides automatic compensation for the nonlinearity of the normal condenser charging curve. By virtue of such compensation the charging rate of condenser I02 is made perfectly linear with respect to time. Due to the action 'of tube I03 the discharging of condenser I02 occurs substantially instantaneously, and hence, the charging and discharging voltage appearing on condenser I02 has a so-called saw-tooth characteristic.

The saw-tooth voltage so created across eondenser I02 is impressed through condenser I00 on the horizontal deflecting plates of the oathode ray tube 20. This sawtooth voltage provides a regularly recurring sweep of the traces produced on the screen of the cathode ray tube for viewing the signals preparatory to making a photographic record for which purpose a single sweep is employed.

In order to provide a suitable bias voltage on the horizontal deflecting plates of tube 20 for 21 centering the traces, resistance I01 and potentiometer resistance II2 are provided for connecting the said horizontal deflecting plates to a point of suitable positive or negative potential with respect to ground as may be required. As shown, one terminal of resistance H2 is connected to the positive 90 volt tap on battery BI while the other terminal is connected to the negative 67 volt tap on battery B3. Thus, a potential of 157 volts is impressed across resistance II2. With this arrangement the traces on the screen of the cathode ray tube 20 may be easily shifted from side to side and brought to a desired position by changing the position of contact III along resistance II2.

When the two-gang switch 42 is in its position 0, the terminals of condenser I02 are directly connected together, and the plate circuit of the tube I04 is opened so that no current is then drained from battery B2. shorting the terminals of condenser I02 is provided for discharging the condenser between pictures.

Upon adjustment of switch 42 to its position at the shunt circuit about the condenser I02 is opened and the plate circuit of tube I04 is conditioned so that it may be closed only when the circuit is closed by the push-button 43. The circuit through which condenser I02 is then charged does not include the tube I03, nor resistances I05 and I06. On closing the circuit by push-button 43, the condenser I02 charges to saturation through the pentode I04. Since there is no path through which the charge on condenser I 02 may leak oif the charging action of condenser I02 is not repeated, and consequently, only a single sweep voltage is impressed on the horizontal deflecting plates of cathode ray tube 20.

It is noted that the frequency of the sweep voltage for both the recurrent sweep and the single sweep is varied by changing the bias voltage on the control grid of tube I04. This changes the tube resistance, and therefore, the time constant of the circuit.

By way of example, it is noted that when the tubes I03 and I04 are of the types designated and the various voltages referred to are employed, the various circuit components of the sweep circuit may have the following characteristics:

Resistance I05 megohms 1 Resistance I do 1.5 Resistance I01 do 2 Resistance I08 do 0.5 Resistance II2 do 1.0 Condenser I02 microfarad 1 Condenser I09 do 0.5

The amplifier 09 is primarily a resistance coupled stage and includes both high and low frequency compensation. The high frequency compensation consists of an inductance element or peaking coil 4 in the plate load circuit of tube H included in amplifier 39 while the low frequency compensation is obtained by means of a parallel connected resistance IIS and a condenser I also connected in the plate load of tube H5.

Tube H5, as shown, is of the pentode type including plate, suppressor grid, screen grid, control grid, and filament type cathode elements, and may desirably be of the commercially available type lL4. Energizing current is supplied to the filament cathode from the A battery AI This arrangement for Gil and plate voltage is supplied by the "B" battery BI. The plate circuit may be traced from the 180 volt positive terminal of battery BI through the parallel connected resistance II! and con- As shown, the output circuits of electronic I switches 36 and 21 are both resistance-capacity coupled to the input circuit of amplifier 30. Specifically, the anodes of the tubes in the electronic switches 30 and 31 are respectively connected by condensers II! and I20 to the control grid of tube IIS and the latter is connected through a resistance I2I to the 3 volt negative terminal of battery C2, the positive terminal of which is connected to ground'and thereby to the filament cathode of tube 5. As previously noted, the electronic switches 36 and 31 operate to alternately impress on the input circuit of amplifler 09 vibration signal voltages from the channel 24 and from the channel 25, and as a consequence, the two vibration signal voltages are reproduced during said alternate half cycles in the output circuit of tube II5.

When switch 44 is in its position b, the output circuit of tube H5 is resistance-capacity coupled to the vertical deflecting plates of the cathode ray tube 20 by means of a condenser I22, a resistance I23 and a potentiometer resistance I24 having a contact I25 and one end terminal of which is connected to the negative and grounded terminal of battery BI. The other end terminal of resistance I24 is connected to the positive volt tap on battery BI. Potentiometer resistance I24 is provided for placing a suitable bias voltage on the vertical deflecting plates of tube 20 for vertically adjusting the positions of the two vibration signal voltage traces produced on the screen. It is noted that variation in the position of contact I25 along resistance I24 is operative to produce a corresponding variation in the vertical position of both of the vibration signal voltage traces on the cathode ray tube screen. The desired vertical displacement of and separation of the two vibration signal voltage traces is accomplished by applying different biases on the control grids of the tubes in the electronic switches 26 and 31 and also by applying diiferent screen grid voltages to said tubes, as previously explained.

Upon adjustment of switch 44 to its position 0, the output circuit of tube H5 is disconnected from and the output circuit of the marking signal generator 4| is resistance-capacity coupled to the vertical deflecting plates of the cathode ray tube 20 by means of the aforementioned condenser 90, resistance 99 and potentiometer resistance I00. Potentiometer resistance I00 and its associated adjustable contact IOI are provided for applying a suitable bias to the vertical defleeting plates for vertically shifting the position of the marking signal trace on the screen of the cathode ray tube. Preferably, the contact MI is so adjusted along the length of resistance I00 that the marking signal trace, and as photographed, appears on the screen below both of the vibration signal voltage traces, as is illustrated in Fig. 8, and wherein curves SI and S2 represent the two vibration signal voltage traces and gurve M2 represents the marking signal voltage race.

The cathode ray tube 2| may be of the commercially available type 902 and includes in addition to the aforementioned horizontal and vertical deflecting plates, the usual first and second anodes. a control grid, a cathode, and a heater filament. Energizing current is supplied the heater filament from a 6 volt "A" battery Al. Suitable voltages are supplied both of the anodes of tube 20 from the battery BI which also serves to provide biasing voltage for the control grid. In order to obtain the different voltages needed for the anodes and the control grid, a voltage divider resistance, having one terminal connected to the positive and grounded terminal of battery B2 and its other terminal connected to the negative 540 volt battery terminal, is provided. The voltage divider resistance is shunted by a fixed resistance I29e and includes in series fromits positve to its negative terminal a resistance I26, a'potentiometer resistance I21, fixed resistances I20, I200, I29b, and I290 and a pair of parallel connected potentiometer resistances III and I 32. Potentiometer resistance I2'I is provided with an adjustablecontact I20 and is utilized for the purpose of varying the voltage impressed on the second anode of the cathode ray tube as required to focus the cathode ray beam on the screen of the tube. The second anode is connected to contact I20 which is adjustable along resistance I21, and the cathode is connected to the negative end of resistance I29. The first anode and also one plate of each pair of the vertical and horizontal deflecting plates are connected to each other and also to the grounded terminal of resistance I20, which terminal is connected to the positive terminal of battery B3.

Potentiometer resistances I30 and I82 are provided for the purpose of adjusting the intensity of the cathode ray'beam and are arranged to be selectively connected in circuit between the cathode and control grid of tube 20 by means of a two position switch I34 which comprises a part of the aforementioned function switch. In position b of switch I contact III movable along resistance I30 is connected to the control grid of tube 20 while contact I" is connected to the control grid when switch I" is in its position c. Contact Ill is so adjusted along resistance I30 that the intensity of the cathode ray beam is sufficiently high to permit the recurrent sweep of the beam for visual observation without causing any damage to the screen. Accordingly, when it is desired to observe the traces on the screen preparatory to making a photographic record thereof, switch I is adjusted to its position b.

The potentiometer resistance I32, along which the contact In is movable, is provided for increasing the intensity of the cathode ray beam while photographing the traces on the screen. While photographing, only a single sweep of the beam occurs, and therefore, the beam may then be adjusted to a very high intensity without resulting damage to the screen. Considerable damage can be done on the recurrent sweep, however, when the beam intensity is high. Accordingly, it is desirable to provide the two intensities of the beam since the high intensity beam is needed for making the photographic record and inasmuch as a beam of lower intensity is satisfactory for observation of the traces.

Resistances I29b and I290 and the associated switch I20d for selectively shunting out those resistances are provided for the purpose of maintalning the traces produced upon the screen of the cathode ray tube at a' substantially uniform and readily visible intensity notwithstanding the tendency for the said traces to become less visible as the sweep frequency provided by generator 40 is increased. To this end the switch I2ld is mechanically connected to switch H0 and is arranged to be adjusted to its positions I), c and d in correspondence with the switch III. Thus. when switch III is in its position. b, providing the lowest sweep frequency, switch I29d is in its b position also. when switch Ill is adjusted to its c and d positions, effecting in each case an increase in the sweep frequency, switch I2 is correspondingly moved to its positions 0 and d to shunt out resistance I200 when in its position c and to shunt out resistances I200 and I20d in its position d. In each case a decrease in the negative bias impressed upon the control grid of tube 20 is effected. This decrease in negative grid bias tends to produce an increase in intensity of the cathode ray tube beam which compensates for the tendency of the beam to become less visible as the sweep frequency is increased.

' When tubes 20 and II! are of the respective types 902 and 1L4 and the battery voltages mentioned are employed, the various circuit components of the amplifier a and the energizing and control circuits for the cathode ray tube 20 may have the following characteristics:

Resistance Iii --ohms 20,000 Resistance III do 30,000 Resistance I23 megohm 0.5 Resistance I24 do 1 Resistance I26 do 0.4 Resistance I21 do 0.1 Resistance I2! do 0.2 Resistance I200 "ohms" 500 Resistance I20b do 50,000 Resistance I200 do 50,000 Resistance I29e do 10,000 Resistance Ill do 20,000 Resistance I82 do 20,000 Condenser Ill microfarads l6 Condenser I22 do- 0.05

Inductance element II4 millihenries 2.5

In Figs. 9, 10, 11 and 12 I have shown an instrument embodying the circuit arrangement described in connection with Figs. 3-6 and which incorporates suitable control devices, adapted to be operated during flight, for adjusting the various switches, for visually observing the vibration and marking signal traces on the screen of the oscillograph to determine what adjustments are required and what effect the adjustments made have on the oscillographic pattern, and for making a photograph of the screen. This instrument constituting the preferred embodiment of my invention is completely self-contained and includes all of the batteries and a camera capable of making 24 records as well as all of the circuit components shown in Fig. 3.

Referring now to Figs. 9 and 10, it will be seen that the instrument is wholly contained within a casing designated by the character I and which may be composed of aluminum or other lightweight material having the necessary rigidity. The instrument includes three separate compartments formed by channel members Ill and Ill which add strength to the instrument casing. In Fig. 9 a portion of the upper panel or cover Ill has been broken away to reveal the channel members I and I3! and the compartments III, III and I formed thereby. Pref- 25 erably, the casing I35 is so designed that the cover I" and the side walls may be readily removed to permit easy access to the components contained in the various compartments.

The electronic amplifiers 21, 29, 3|, 33 and 39, the integrators 28 and 32, the electronic switches 35 and 31, the multi-vibrator 38, the marking signal generator H, and the sweep frequency generator 43 are all arranged within the compartment I38. It is noted, however, that the various switches for adjusting the electrical circuit components are supported by the upper panel I of the instrument and are provided with exteriorly disposed knobs for facilitating adjustment thereof.

The cathode ray tube 20. the hinged viewing mirror 22, the camera 3 including shutter 5, and the film 8, which constitutes one of the films in a film pack I42 of the magazine type, are all contained within the compartment I39 while all of the various batteries required for energizing the instrument, a few of which may be seen in Fig. 9, are contained within the compartment As shown, the compartment I39 is provided with a hood I43 which may be held by removable screws to the side of the instrument for making the compartment I39 long enough to accommodate the cathode ray tube 20 and to provide proper focussing of the camera 3. The cathode ray tube 20 is supported at this end of the instrument by a socket I44, which, in turn, is mounted on a bracket I45. The bracket I45 is supported by the channel members I35 and I31. At its other end the cathode ray tube 20 is held to prevent displacement thereof by a supporting cylindrical member I45 carried by a plate I41 through a circular opening in which the member I46 extends. The end of member I46 engaging the cathode ray tube 20 is shaped as shown in Fig. in order to permit easy replacement of the cathode ray tube 20. A cover plate I48 fastened to the top panel I of the instrument by removable screws is provided to facilitate such replacement.

When it is desired to remove the tube 20, the plate I48 is removed, the tube is pushed to the left against the restraining force of the bracket I45 supporting the tube socket in order to disengage the screen end of the tube from the cylindrical supporting member I45, and the tube 29 may then be lifted out through the opening in the panel I4I, the tube being simultaneously given movement to the right in order to effect disengagement with the socket I44. Similar operations are required in order to insert a new cathode ray tube in the instrument.

Although not shown in the drawing, the switches 42, 44, 91 and I34 preferably are all ganged together and comprise the function switch aforementioned. The function switch" is actuated by a single knob designated by the character I49 and is provided with a scale having six different positions which in Fig. 9 may be labelled, reading in a clockwise direction, as

,, follows (1) View signals (2) View marking signal (3) Discharge (4) Print signals (5) Discharge (6) Print marking signals The table immediately following shows the positions assumed by the switches 42, 44, 91 and I34 as the function switch is adjusted to each of its six positions.

To the attainment of such operation the switches 42, 44, 91 and I 34 preferably comprise separate sections of a ganged multiple point switch having. six operative positions. Points on the separate sections are directly connected to each other as required to cause the various switches to effect the above sequence of circuit connections as th gang switch is successively adjusted into each of its six positions.

As shown in Fig. 9, the instrument is also provided with suitable knobs I50, I5I, I52, I53 and I54 for respectively accomplishing the desired adjustments of the attenuators 26 and 30, the connection of the integrators 28 and 32 into and out of the channels 24 and 25, and the adjustments of the frequencies of the marking and sweep voltages to a value commensurate with the frequencies of the vibration signal voltages. A multipoint power switch I55 is also provided for disconnecting the various battery circuits when the instrument is not in use. Those skilled in the art will readily understand how the switch I55 may be connected in the circuit of Fig. 3 to accomplish this result.

Suitable designations are placed on scales disposed in cooperative relation with the knobs I5Il-I55 in order to facilitate use of the latter. Thus, the scales associated with knobs I50 and I5I designate the ratios of the attenuator output voltages to the full amplifier voltage gain for each of the knob positions, the scales associated with the knobs I52 and I53 indicate whether the integrators 28 and 32 are connected into or disconnected from the channel 24 or 25 individual thereto, the scale associated with knob I54 indicates the marking signal frequency and also the sweep voltage frequency, and the scale associated with the knob I55 indicates whether the power is turned on or oil.

Push button 43 for efiectuating the single sweep of the cathode ray beam extends through the upper panel I of the instrument in such a manher as to be easily accessible for manipulation. In addition, a viewing hood I55 for observing the traces on the cathode ray tube screen and slots I51 and I58 for respectively accommodating the film pack I42 and a spare pack I59 are provided in the panel I4I, as shown. Each film pack includes 12 films which may be successively exposed by moving the slide provided with each pack. When all of the films of pack I42 have been exposed, it is removed from slot I51 and pack I59 is inserted therein and its films successively exposed. The exposed pack I42 may be lodged in slot I58 while the second pack I59 is being exposed. Thus, the instrument is capable of making 24 successive photographic records.

The viewing hood I58 comprises a hinged plate provided with a tab I50 which may be easily grasped for lifting the plate up and thereby opening the hood to permit an observer to look into the interior of the instrument to view the pattern on the oscillograph screen which is reflected through the opening bymirror 22. Suitable latch means assume of a type known in the art are provided to hold the hinged plate stationary when the latter is adjusted to its open (viewing) and closed (photographing) positions. In Figs. 9 and 10 the hinged plate is shown in its closed position. The hinged plate is also provided with a projecting part desig-- nated by the character Ill which is disposed in cooperative relation with a movable pin Ill provideo for effecting angular displacement of the viewing mirror 22 from the optical path between the screen of the cathode ray tube II and the lens 4 of the camera l when the viewing hood Ill is closed. As shown in Figs. 10 and 11, the mirror ll is carried by a U-shaped bracket Ill which is arranged to be angulariy deflected. being supported by its legs on bearings Ill and Ill which, in turn. are fastened to plate I41. Mirror ll is glued or oherwise fastened to the inside bottom edge of the bracket Ill so that as the latter is moved counterclockwise through a predetermined angle the mirror is moved from a position wherein it reflects the face of the oscillograph screen through the viewing hood Ill to a position wherein the mirror is out of the range of the optical path between the osciilograph screen and the lens I of camera l.

Bracket Ill is biased for deflection in the clockwise direction into its viewing position by means of a coiled spring Ill one end of which bears against the plate I41 and the other end of which is fastened to one leg of the bracket. The means for deflecting the bracket in a counterclockwise direction and thereby for moving the mirror ll out of the optical path to the camera when the viewing hood Ill is closed includes a part I" projecting from the last mentioned leg of the bracket Ill, a link Ill, and a member Ill which is pivoted at one end on the plate I" and rests at a point intermediate its ends on the pin Ill. One end of the link Ill is pivoted on the projecting part Il1 and its other end extends through a guide member I" and rests on a bent over por tion of the free end of the member Ill. tending to eflect clockwise movement of the member Ill against the restraining force of the pin Ill. The guide member I1! is fastened to the plate I". The various parts are so arranged that when the viewing hood Ill is closed the pin Ill is pushed in by the projection Ill and causes the member Ill to deflect in a counterclockwise direction into the position shown in Figs. 10 and 11. In so deflecting the member Ill bears against the associated end of the link Ill and causes the bracket Ill to be deflected in a counterclockwise direction against the restraining force of the coiled spring Ill. Such movement of the bracket Ill I is eiiective to move the mirror 22 out of the optical path between the cathode ray tube ll and the camera I. when so adjusted the various parts are held against movement by the latch means provided on the viewing hood Ill.

when the viewing hood Ill is opened the bracket Ill is deflected by the coiled spring Ill in a clockwise direction. since the restraining force of the pin Ill has been removed, and causes the various associated parts to similarly deflect until a shoulder "I provided on the pin Ill abuts against a bent over portion of the plate I41, which in turn is fastened to the under side of the top panel Ill of the instrument. In this position of the parts the mirror 22 reflects the face of the osciliograph screen through the viewing hood Ill thereby permitting an observer to view the traces on the screen.

As is best seen in Fig. 10, the shutter l is pivoted for rotation at one end on a shaft I12 with which it is rigid and which is carried by the channel members forming the three compartments and is arranged to be deflected in a clockwise direction from the position shown to expose the film l. The means for deflecting shutter l include an arm I1l which is rigid with shaft "l. a link I14, a bell crank lever I15 pivoted at I1l on one of the-channel members, and a push pin I11 provided with a knob I1l hereinafter termed the camera shutter knob. A U-shaped bracket I" through the arms of which the push pin I11 extends is provided for guiding the pin I11 and a shoulder Ill. A cooperating spring Ill arranged. as shown, between the arms of the bracket I1! is provided for biasing the push pin into the position shown. In that position of the push pin the bell crank I15, one end of which bears against the end of the push pin and the other end of which provides a pivot point for one end of the link I14, is biased to its extreme counterclockwise position by a spring Ill connecting the bell crank lever I15 to the shaft I12. The other end ofthe link Ill is connected to the movable end of arm I1l.

with the parts in the position shown the shutter I prevents exposure of the film l but upon deflection of the bell crank I15 in a clockwise direction against the restraining force of the spring Ill the shutter l is deflected by the action of link I" and arm Ill in a clockwise direction to the position wherein it is out of the optical path between the fllm l and the face of the oscillograph screen. thereby exposing the fllm. This result is accomplished by pushing in on the camera shutter knob Ill against the restraining action of the spring Ill. When the camera shutter knob I1l is released the bell crank lever Ill and consequently the shutter l are actuated in a counterclockwise direction to their positions shown in dashed lines by the spring Ill. While switch ll has been shown as being externally accessible for separate manipulation, it will be understood that this switch may be mechanically related to push pin I11 and knob I18 so as to be automatically closed when the knob I1l has been depressed to'expose the film.

As shown in Fig. 9 and in more detail in Fig. 12 the potentiometer resistances Ill, Ill, Ill, I21. Ill and Ill are mounted on the channel separating the compartments Ill and Ill at a position adjacent the cathode ray tube ll. The shafts of the potentiometer resistances extend into the compartment Ill and are each provided with a kerf suitable for screw driver adjustment from that compartment. The adjustments to the potentiometer resistances, although easily made by virtue of this construction, are not intended to be made during actual flight. It will be understood, however, that. if desired, the various potentiometers may be mounted otherwise and provided with knobs available for adjustment from the exterior of the instrument.

Compartment Ill of the instrument contains all of the batteries needed for the operation of the instrument over a period of at least 8 hours before replacement is necessary. The A batteries Al. Al and Al. which are each comprised of i k-volt units, may desirably be of the commercially available Burgess type ZFBP. while the A battery Al, comprised of two 3-volt units. may be of the Burgess type 2F2H. The "B" battery BI comprised of four 45-volt units. may be of the Burgess type XXlO; the 3" battery B! may be comprised of four 45-volt units of the Burgess type xxso and one fi'l -volt unit of the Burgess type XX45. The "B" battery Bl. comprised of eight 67 -volt units, may be of the Burgess type XX45. The C"battery CI and a portion of the units of the C battery C2 may be comprised of two 3-volt units of the Burgess type 5540. The remaining units of battery C! may be comprised of a 'l -volt unit of the Burgess type 5540. If desired, the batteries CI and C2 may be made up of a suitable number of Mallory bias cells.

The sequence of operation of the preferred embodiment of my invention is as follows:

1. Switch the integrator knobs I52 and I53 to the desired position.

2. With the hood I58 open and the function switch knob I49 in the position marked Viewing signal" adjust the attenuator knobs I50 and Iii for the desired amplitude of the vibration signal traces'as seen through the viewing hood I and adjust the sweep frequency knob I54 for a sweep frequency commensurate with the frequency of the vibration signals.

3. Check the marking signal by adjusting the function switch knob I49 to the position marked View marking signal.

5. Turn the function switch knob I49 to the position Print signal" passing only momentarily on the discharge" point.

6. Depress the camera shutter knob I'l and close the push button switch 43. Release both immediately.

'1. Adjust the function switch knob I49 to the "Print marking signal position pausing only momentarily on the discharge point.

8. Again depress the camera shutter knob I18 and close the push button switch 43. Release both immediately.

Subject matter disclosed but not claimed herein is disclosed and is being claimed in the application Serial Number 593,038, filed concurrently herewith, of Donald C. Culver, Rudolf F. Wild, Thomas R. Harrison and Walter P. Wills.

While, in accordance with the provisions of the statutes, I have illustrated and described the best forms of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is as follows:

l. A device to compare the frequency. phase and amplitude of two electrical signals comprisin an electronic amplifier to amplify each of said signals, a cathode ray tube having vertical deflecting plates and horizontal sweep deflecting plates, an electronic switching device to alternately impress at a predetermined frequency during mutually exclusive intervals the amplifled quantity of each of said signals on the said vertical deflecting plates comprising two electron discharge tubes each having anode, cathode. screen, and first and second control electrode elements, means to impress said signals between the second control electrode and cathode elements of an associated one of said tubes, means source of energizing voltage, circuits including said voltage source and connecting the anode and cathode elements of each of said tubes, connections from the screen elements of each of said ously occur, and switching means operative in one condition to couple the anode and cathode elements of both of said tubes to said vertical deflecting plates and to connect the output circuit of said first relaxation oscillator to said horizontal sweep deflecting plates and operative in a second condition to connect the output circuits of said first and second relaxation oscillators to said horizontal sweep and vertical deflecting plates, respectively.

2. An electronic switching device for alternately impressing-during mutually exclusive intervals a first electrical signal and a second electrical signal on the beam deflection plates of a cathode ray tube employin electrostatic beam deflecting plates comprising two electron discharge tubes each having anode, cathode, screen, and first and second control electrode elements, means to impress the first electrical signal between the second control electrode and cathode elements of one tube, means to impress the second electrical signal between the second control electrode and cathode elements of the ode and cathode elements of both of said tubes to terminals adapted to be connected to the beam deflecting plates of a cathode ray tube, connections from the screen elements of each of said tubes to points of positive potential on said voltage source, the screen element of the second tube being connected to a point of greater positive potential than the screen element of said one tube, and relaxation oscillator meansto impress voltages out of phase between the first control' electrode and cathode elements of said tubes comprising two other electron discharge tubes each having anode,- suppressor, screen,

control electrode and cathode elements, circuits including said voltage source for energizing the screen and anode elements of said other tubes, capacitors cross-connecting the anode and control electrode elements of said other tubes, 2. resistor connected in each of the anode circuits of said other tubes, a biasin resistor for said control electrode elements of said other tubes connected between the cathodes of said other tubes and the negative terminal of said voltage source, and a resistor connected between the control electrode element of each of said other tubes and a positive potential point on said source. 

